A hole for receiving a wire electrode therethrough, namely, an initial hole, must be formed at a predetermined position on a workpiece prior to wire-cut electrical discharge machining. The initial hole must be formed at a position as near as possible to the wire guide of the wire-cut electrical discharge machine. When an initial hole is formed near a wire-cut starting position, the wire electrode can be inserted through the initial hole immediately after the initial hole has been formed, to start wire-cut electrical discharge machining.
However, the conventional initial hole forming means is disposed as far away as possible from the wire electrode guiding unit of the electrical discharge machine in order to prevent interference between the initial hole forming means and the wire electrode guiding unit. Consequently, in some cases, the wire electrode guiding unit cannot be moved relative to the workpiece to insert the wire electrode through the initial hole formed in the workpiece by the initial hole forming means. That is, inconveniently, the initial hole can be formed in the workpiece only within a particular limited area. Accordingly, it is desired to dispose an initial hole forming device adjacent to the wire guiding unit. However, when an initial hole forming device is disposed adjacent to the wire guiding unit, the wire guiding unit may interfere with the initial hole forming device in that the wire guiding unit is displaced from the normal position for forming a tapered hole or the like by the wire electrode. Therefore, such disposition of the initial hole forming device requires an appropriate interference preventing means to prevent damage to the machine.